Helper T cell activation leads to differentiation into multiple possible effector lineages. Each of these lineages is optimized for generating a productive immune response against specific classes of pathogens. The Th17 lineage is a recently defined subset that provides immune protection against extracellular bacteria and fungi at mucosal surfaces. Inappropriate activation of these cells is associated with a variety of inflammatory disorders. The overall goal of the project is to elucidate the regulation of the function and differentiation of this subset, providing understanding from which effective interventional, immunomodulatory therapies can be developed to improve immune responses to infection and cancer, treat inflammatory disorders, and improve vaccine efficacy. Th17 cells are defined by secretion of the cytokine IL-17 and also produce IL-17F, which are transcribed from neighboring IL-17A and /L-77F genes. We therefore designed this project to comprehensively identify and characterize the regions of extragenic DNA neighboring the IL- 17A-IL-17F locus that function to regulate IL-17 expression. Three specific aims are proposed to accomplish our research goals. In Aim 1, we will identify regulatory elements utilizing genome-wide profiling for DNase I hypersensitivity sites, and analyze chromatin immunoprecipitation for activating and repressive histone modifications. In Aim 2, we will use immunoprecipitation for TFs to determine which of these identified regulatory elements, are direct targets of T cell lineage-specific TFs. In Aim 3, we will characterize the in vitro function of identified regulatory elements by transient transfection assays utilizing a luciferase reporter system. This project represents the first examination of IL17A-IL17F locus regulation in human Th17 cells, and the first comprehensive profiling of these c/s-regulatory elements in any species. Understanding the regulation of the important IL17A and /Lf7F genes will lead to the intelligent modulation of adaptive immunity, providing novel treatments for infection, cancer, and inflammatory disorders. CD4+ T cells function as potent regulators of the adaptive immune response, and we propose a comprehensive approach to studying the function and generation of Th17 cells, a type of CD4+ T cell that is a particularly potent inducer of inflammation, especially at mucosal surfaces such as the lungs.